Internal combustion engines utilize emission control devices to reduce emissions from the engine. The emission control devices may be filters, catalysts, and other suitable device for removing unwanted gases, particulates, etc., from an engine exhaust stream. Some emission control devices inject reductants, such as urea or ammonia, into the exhaust system upstream of a catalyst to convert nitrogen oxides into diatomic nitrogen, water, etc., to reduce the amount of nitrogen oxides released to the atmosphere. The reductant spray and the catalyst work in conjunction to enable nitrogen oxide conversion.
To aid in nitrogen oxide conversions in the catalyst, various approaches are provide to mix the reductant spray in the exhaust stream to promote even distribution of the reductant. One approach is described in US 2010/0107614 using various mixing devices with a specific injector configuration.
The inventors herein have recognized some disadvantages of the above approach related not only to manufacturability, but also to how the various features work together in combination. In addition to packaging and manufacturability issues, the overall flow path and mixing interactions between the injector and various mixing devices along the exhaust flow path can result in unintended consequences that degrade overall atomization under certain temperature and flowrate conditions.
To address at least some of these issues, one approach provides a mixing system. The mixing system includes a housing defining a boundary of a mixing conduit including an expansion section with an injector mount and a reductant diverter extending into the conduit upstream of the injector mount in the expansion section. The mixing system further includes an atomizer with openings positioned in the housing and a helical mixing element positioned in the housing.
The atomizer may decrease the size of the reductant droplets in the exhaust stream and work in cooperation with the diverter positioned in the expansion region. Because the expansion region enables a reduction in pressure and flow velocity, the diverter takes advantage of the change in flow conditions to aid in the injector droplet mixing where the atomizer, being at the end of the expansion region in one example, can then further enhance the mixing and prepare it for entrance into the downstream helical mixing region. As a result, nitrogen oxide conversion in a catalyst positioned downstream of the mixing system may be improved. Thus, not only does the helical mixing element increase the turbulence in the exhaust gas and promote more even distribution of the reductant spray in the exhaust gas, it does so with a mixture that has been especially prepared for such an operation. It will be appreciated that the atomizer and helical mixing element work in conjunction with the expansion region and diverter to promote mixing of the reductant spray in the exhaust stream to improve operation of a downstream catalyst.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.